Vapor-liquid equilibrium in NH3-CO2-H2O system at high pressures has been studied. The UNIQUAC-NRF model for this system was extended by using the Goppert 4 maurer reported datas. Since the system contains molecules and ionic species the binary interaction parameters considered, where those are of molecule-molecule, molecule-ion and ion-ion types. These interaction parameters are taken as constant values in UNIQUAC-NRF, which are not accurate. In this work the mentioned parameters have been considered as function of temperature in quadratic form. By applying an optimization mathematical program to the UNIQUAC-NRF model and experimental data reported by Goppert and Maurer the model parameters were obtained in term of temperature. The results of this model with the new parameters show good agreement with experimental data.

The determination region of solubility of methanol with gasoline of high aromatic content was investigated experimentally at temperature of 288.2 K. A type 1 liquid-liquid phase diagram was obtained for this ternary system. These results were correlated simultaneously by the UNIQUAC model. The values of the interaction parameters between each pair of components in the system were obtained for the UNIQUAC model using the experimental result. The root mean square deviation (RMSD) between the observed and calculated mole percents was 3.57 % for methylcyclohexane + methanol + ethylbenzene. The mutual solubility of methylcyclohexane and ethylbenzene was also investigated by the addition of methanol at 288.2 K.

A thermodynamic consistent model was developed for representing vapor-liquid equilibria in acid gases (H2S, CO2)-alkanolamine-water systems. The model accounts for both chemical and phase equilibria in liquid and gas phases, respectively. The activity coefficient of species was calculated using Pitzer-Debye-Huckel theory for long range interactions and UNIQUAC-NRF model with ion-pair approach for short range interactions. The energy interaction parameters of UNIQUAC-NRF were obtained for MDEA+H2O+CO2 and MDEA+H2O+H2S systems. The results of the model are in very good agreement with the experiment.

Etodolac, Lamotrigine, diazepam, and clonazepamine are four important drugs in the pharmaceutical industry that optimizing the solvent concentration in the least amount can reduce the cost and toxicity of these drugs. Due to the lack of thermodynamic modeling based on the activity coefficient equation in previous studies for solubility of Etodolac, Lamotrigine, diazepam, and clonazepamine in aqueous solution, in this study, based on thermodynamic equations and UNIQUAC model, their solubility is optimized with the presence of water and ethanol. Based on the objective function defined, the error rate of the model optimization value was acceptable for each system. The results of this study can be used to better understand the intermolecular reaction of Etodolac, Lamotrigine diazepam, and clonazepamine in the presence of ethanol and water solvents. Also, the importance of the optimization results of this study in order to design a computer program to predict the solubility of these drugs is significant.

In this work, an electrolyte-UNIQUAC model was developed by replacement of Boltzmann weight binary interaction parameters by the nonextensive Tsallis weight. A summation of the long-range electrostatic term (Debye-Huckel equation) and a short-range interaction term were considered in the calculation of thermodynamic properties. A framework proposed by Chen et al. was employed for the derivation of the local mole fractions. Application of the nonextensive theory increased the degree of freedom of the present model (T-E-UNIQUAC). Furthermore, the strength of the model lies in its ability to calculate individual activity coefficients of ions. The applicability of the T-EUNIQUAC model were tested using aqueous electrolyte solutions, and subsequently, results were compared with Messnaoui, Chen and Pitzer models.

The UNIQUAC activity coefficient model is extended to predict solid-liquid equilibrium of isotactic crystalline poly (I-butene), iPBu-I, in different organic solvents. The UNIQUAC activity coefficient model used in this work is based on the concept of group contribution and consists of combinatorial, residual and free volume terms. To account for branching of atom groups in the monomer structure of the polymer, a correction factor has been applied to the surface parameter of combinatorial and residual terms. Use of this correction factor has significantly improved the accuracy of the model and shows that the proposed activity coefficient model is a proper model for solid-liquid equilibrium calculation in polymer solutions.

In the present study, in order to predict the activity coefficient of inorganic ions, 12 cases of aqueous chloride solution were considered (AClx=1, 2; A=Li, Na, K, Rb, Mg, Ca, Ba, Mn, Fe, Co, Ni). For this study, the UNIQUAC thermodynamic model is desired and its adjustable parameters are optimized with the genetic+particle swarm optimization (PSO) algorithm. The optimization of the UNIQUAC model with PSO+genetic algorithms has good results. So that the minimum and maximum electrolyte error of the whole system are 0. 00044 and 0. 0091, respectively. For this study, a temperature of 298. 15 and a pressure of 1 is considered. Also, in this study for the electrolyte system, the Artificial bee colony (ABC) algorithm, and Imperialist competitive algorithm (ICA) has been studied. The results showed that the Artificial bee colony algorithm has a lower accuracy than the genetic + PSO algorithm. The minimum concentration was 0. 1 Molality and the maximum concentration was 3 Molality. Based on the results, the activity coefficient of LiCl, NaCl, KCl, RbCl + H2O, MgCl2, CaCl2, BaCl2, MnCl2, FeCl2, CoCl2 NiCl2 depends on the ionic strength of the electrolyte system.